For me it has to be Osher Williams' debut in 1979, a League Cup match v Crystal Palace (who I think were top fight at the time?).
Osher ran rings around their full-back, none other than the great Kenny Sansom. Helped us to a 1-1 draw.
In the replay (I couldn't believe the prices in London to watch a football match, something like £3.50 IIRC) - we lost 7-0.
At one point John Rutter was hit by the ball in the face, and it appeared to knock him out. Sansom then mocked him for it later in the game, which didn't seem very classy, given the humiliation he had suffered a week before.
Of course, Osher hardly had a kick of the ball in this game, but went on to be a County favourite, and (to me at least) a County legend